Bolton served as US Ambassador to the UN from 2005 to 2006, and is a frequent Fox News contributor.

During the presidential transition, Donald Trump reportedly passed on selecting former US ambassador to the UN John Bolton as his top national security adviser because of Bolton's eccentric mustache.

When Roger Ailes, the ex-chairman of Fox News and longtime Trump ally, suggested Trump appoint Bolton to the coveted Cabinet position, then incoming White House Chief Strategist Steve Bannon fired back, according to excerpts from Michael Wolff's upcoming book about the Trump presidency.

"He's a bomb thrower. And a strange little f---er," Ailes reportedly said. "But you need him. Who else is good on Israel? [Michael] Flynn is a little nutty on Iran. [Rex] Tillerson just knows oil."

Bolton served as the US Ambassador to the UN for just over a year from 2005 to 2006 under President George W. Bush. His tenure was fraught with controversy because of his confrontational approach to foreign relations and previous criticisms of the UN.

But his abrasive style, according to Ailes, is what might have made Bolton a logical choice considering Trump's own image as a disrupter-in-chief.

"[Bolton] got in trouble because he got in a fight in a hotel one night and chased some woman," Ailes reportedly said, referring to a 1994 incident that allegedly took place in a Moscow hotel and later resurfaced during Bolton's UN ambassadorship confirmation hearings in 2005.

Bannon replied: "If I told Trump that, he might have the job."

As rumors swirled that Trump was considering Bolton for a top Cabinet post, the former diplomat took to Twitter to double down on his signature mustache, reassuring critics that it was not going anywhere even if he was offered a job.

"I appreciate the grooming advice from the totally unbiased mainstream media, but I will not be shaving my #mustache," Bolton said in a tweet.

Trump ultimately nominated Michael Flynn to become his national security adviser. After his interactions with Russian officials became public early last year, Trump fired him in February, just 25 days into Flynn's tenure. Flynn has since pleaded guilty to lying to the FBI.